Hollow drive shaft with integrated vibration absorber

ABSTRACT

An effective reduction of vibration overshoots is intended to be effected in a drive shaft, which is configured as a hollow shaft ( 8 ), with simple means at the particular vibration maximum (vibration antinode). 
     A vibration absorber ( 2 ) is arranged within the hollow shaft ( 8 ) and includes a damping mass (absorber mass) ( 4 ) and an elastic coupling element ( 6 ). The absorber mass ( 4 ) is operatively connected to the inner wall of the hollow drive shaft ( 8 ) via the elastic coupling ( 6 ). The absorber mass is configured to be rotationally symmetrical and axially symmetrical and has, at its center, a constriction ( 12 ) for accommodating the elastic coupling element ( 6 ). 
     For use as a drive shaft (hollow shaft) ( 8 ), which is built in in the vehicle transverse direction, and for use as a drive shaft ( 8 ) (cardanic shaft configured as hollow shaft) which is built in in the vehicle longitudinal direction.

FIELD OF THE INVENTION

The invention relates to a hollow drive shaft having an integratedvibration absorber especially for a motor vehicle.

BACKGROUND OF THE INVENTION

In a motor vehicle, the torque from a drive motor (especially aninternal combustion engine) is to be transmitted via a flywheel, aclutch, a transmission, a differential (change-speed gear) to a drivewheel.

If two of the above-mentioned components are arranged spatially apartfrom one another, then they are to be connected to each other by a driveshaft for the torque which is to be transmitted from one component tothe other component. Drive shafts of this kind tend to oscillate andvibrate in an unwanted manner.

In “Automobiltechnische Zeitschrift” of Jun. 6, 1976, starting at page259, a drive shaft is described which is surrounded by a tubefunctioning as an ancillary support. A bearing having a rubber ring ismounted between the shaft and the tube and is intended to insulateagainst vibrations. This kind of vibration damping has been determinedto be completely inadequate. In this connection, reference can be made,for example, to German patent publication 2,747,225, column 1, lines 38to 51.

German patent publication 1,178,303 in combination with German patentpublication 1,113,367 describe a drive shaft configured as a metal rodwhich is surrounded by vibration dampers at specific locations.

The problem of this kind of massive drive shaft having external dampersis that these external dampers have a relatively large radius. Thesevibration absorber masses are also not protected against externaleffects such as dirt and damage because they are mounted outside on themassive drive axle.

Besides vibration dampers for complete shafts wherein the vibrationdamper is mounted outside on the drive shaft configured from solidmaterial, vibration dampers are also known which are mounted within ahollow supporting tube fixed against rotation and surrounding themassive drive shaft.

German patent publication 1,755,860 covers a vibration absorber of adrive shaft wherein the vibration absorbers are configured in the formof annular-shaped rubber springs burdened by mass. These rubber springsare disposed between the drive shaft and, if required, a hollow tubeserving as protection. The hollow tube is optionally provided and isintended to serve, if needed, as an additional vibration absorber mass.This hollow tube is more or less rigidly connected to the engine blockand possibly also to other vehicle parts. For this reason, a mostinadequate reduction of the vibrations emanating from the engineresults.

A trouble-free decoupling of the vibration absorber mass and othermasses is not possible with this configuration.

A complete separation of massive drive shaft and hollow tube is providedin the arrangement described in German patent publication 2,747,225.However, here a vibration absorber mass is only mounted on the hollowtube. It is, however, the drive axle itself which preferably tends tounwanted vibrations. For this drive axle, no damping measures whatsoeverare provided so that such a vibrating axle can transmit its vibrationsvia the components (engine, transmission, et cetera) more or lessunhindered to the vehicle. These components are connected force-tight tothe drive axle.

Hollow shafts are also known. In view of the teaching which can be takenfrom the state of the art described above, the person of skill wouldarrange the required damping on the outer side of the hollow shaft. Theperson of skill would then be confronted with the difficulties knownfrom massive drive shafts.

Vibration dampers for hollow shafts have, however, also been suggestedwherein the vibration damper is mounted within the hollow shaft.Proceeding from a simple embodiment comprising matching mass and elasticlayer, German patent publication 3,632,418 describes a vibrationabsorber wherein a matching mass is connected via an elastic covering tothe inner wall of a drive shaft as well as via a further elastic layerto an absorber mass. Apart from the consideration that this absorberarrangement is configured asymmetrically with respect to a crosssection, it exhibits a considerable structural length in the axialdirection. For these reasons, this kind of vibration absorber cannot bemounted on the antinode of vibration of a tube shaft tending to vibrate.The further embodiment wherein a deformable body can be clamped in thehollow shaft likewise has a considerable axial length. Here, the samedisadvantages already mentioned are presented.

SUMMARY OF THE INVENTION

The object of the invention is to achieve an effective reduction ofvibration overshoots at bending resonances with simple means on a driveshaft configured as a hollow axle while avoiding the knowndisadvantages.

The above object is achieved with an arrangement according to theinvention in that the absorber mass, which is located within the hollowshaft, is configured to be rotationally symmetric and has a centerconstriction for receiving the elastic coupling element.

The essence of the invention is a vibration absorber which is mounteddirectly in the hollow drive shaft and thereby reduces vibrationsdirectly at the drive shaft while saving space.

No additional space requirement exists because of the arrangement withinthe tube shaft. The vibration absorber according to the invention can beinexpensively manufactured because of the simple configuration thereof.The elastic coupling element is configured as a rubber ring and exhibitsonly slight longitudinal expansion. In this way, the vibration absorbercan be mounted in a targeted manner on the particular vibration maximum(vibration antinode) of the hollow tube.

Bending vibrations are absorbed with the vibration damper according tothe invention. The vibration damper (vibration absorber) is configuredso as to be axially symmetrical and has only a slight mass. For thisreason, its imbalance is only very slight even in the deflected state.The danger of build up of an imbalance is therefore hardly a concern.

The vibration absorber is configured so as to be compact and, because itis mounted within the hollow shaft, it is reliably protected fromexternal interferences.

Preferably, the vibration absorber is premounted in a slotted sleevethereby facilitating the assembly. Because of a higher pretensioning ofthe rubber, one can work with a reduced inherent stress of the slottedsleeve. The sleeve is a cost-effective metal part.

The sleeve can be selectively made of a material having poor thermalconductivity (for example, plastic) to reduce the temperature loading ofthe coupling element in subsequent processing steps (welding, hardening,lacquering).

The elastic coupling element preferably comprises a material of theelastomer group or a technically like material.

Different resonance frequencies can be realized with different grades ofhardness. The subsequent warming of the elastomer in further productionsteps can be considered (for example, targeted undervulcanization) by asuitable selection of the vulcanizing parameters.

The absorber is preferably so matched that the inherent frequencyamounts to 55% to 85% of the inherent frequency of the shaft. In thisway, the amplitude of the first of the two resonance locations whichresult is less than the amplitude of the second resonance location.

The absorber mass, coupling element and press-in sleeve can beselectively vulcanized one to the other, pressed together or joined toeach other with adhesive.

The positioning in the hollow shaft is ensured by the pressed-in sleeve.A purposeful profiling of the pressed-in sleeve fixes the rubber springand secures the absorber position.

The use of only a single coupling element, which is configured as aspring ring, makes a defined simple press-in possible.

An axial bore or a slit in the coupling element makes a pressurecompensation possible between the hollow spaces of the right and leftshaft halves and thereby prevents unwanted conditions of stress whichcan develop because of the generation of gas when welding on the shaftends.

To avoid wobbling oscillations, a ratio of width of the rubber spring tothe length of the absorber mass of 0.2 to 0.4 has been shown to beespecially suitable. The absorber mass is usually 100 to 200 grams, inextreme cases 50 to 500 grams.

An inherent frequency of the absorber in the range of 70 to 300 Hzresults in combination with an elastomeric damping of 3 to 15°.

The absorber according to the invention can preferably be used startingat a shaft diameter of approximately 20 mm. Here, the diameter of theabsorber mass should be at least 2 mm less than the tube interiordiameter. The mass can be rubberized to prevent knocking noises in thetube.

A further embodiment of this idea is to arrange knocking nubs on theperiphery of the absorber mass.

The damped hollow shaft according to the invention can preferably beused as drive shaft of front-driving vehicles with the drive shaft beingmounted in the transverse direction of the vehicle; or, this dampedhollow shaft can be used as drive shaft mounted in the longitudinaldirection of the vehicle (cardanic shaft configured as a hollow shaft)of rear-driven vehicles with the engine mounted in the front.

BRIEF DESCRIPTION OF THE DRAWING

In the following, the vibration absorber, which is configured, accordingto the invention, within a hollow shaft, is described in greater detailwith respect to an embodiment.

FIG. 1 shows a detail view, in longitudinal section, of a hollow driveshaft having an integrated vibration absorber.

FIG. 2a shows a longitudinal section of a modification of the vibrationabsorber and FIG. 2b shows a cross section of the modification of thevibration absorber of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The vibration damper (vibration absorber) 2 includes a vibration dampingmass 4 and an elastic coupling element 6. Both (4, 6) are disposedwithin a hollow shaft (tube shaft) 8. The mass 4 is operativelyconnected via coupling element 6 to the tube shaft 8. The vibrationabsorber mass 4 is a rotationally-symmetrical and axially-symmetricalstructure referred to the tube axis 10. The vibration absorber mass 4has a constriction 12 at its center for accommodating a coupling element(rubber bearing) 6 which is configured to be ring shaped. In theembodiment shown, a sleeve 14 is located between the rubber bearing 6and the interior wall of the hollow shaft 8. Preferably, this sleeve 14has a slit which facilitates assembly of the vibration damper 2 andpressure compensation. The mass 4 of the vibration absorber 2 iscompletely surrounded by a rubber skin 16.

The coupling element 6 has an axial cutout 6.1 (bore, slot) connectingthe hollow spaces (8.1 and 8.2) on respective ends of the vibrationabsorber 2 to each other.

In the further embodiment of the vibration absorber 2 shown in FIGS. 2aand 2 b, knocking nubs 18 are arranged on the periphery of the absorbermass 4.

The slotted sleeve 14 can be selectively made of a poorly thermallyconducting material such as plastic.

The vibration absorber 2 has a resonant or inherent frequency which ismatched in such a manner that the resonant or inherent frequency of thevibration absorber is 55 to 85% of the resonant or inherent frequency ofthe hollow shaft 8 without the vibration absorber.

The absorber mass 4, the elastic coupling element 6 and the slottedsleeve 14 can be vulcanized to each other.

Alternatively, the absorber mass 4, the elastic coupling element 6 andthe slotted sleeve 14 can be pressed to each other. As still anotheralternative, the absorber mass 4, the elastic coupling element 6 and theslotted sleeve 14 can be joined to each other by adhesive.

As shown, the elastic coupling element 6 has an axial cutout 6.1connecting the hollow spaces (8.1 and 8.20) on respective ends of thevibration absorber 2 to each other. The axial cutout 6.1 can be a boreor a slot.

HOLLOW SHAFT HAVING AN INTEGRATED VIBRATION ABSORBER LIST OF REFERENCENUMERALS

2 Vibration damper, vibration absorber

4 Vibration damping mass, absorber mass

6 Coupling element, coupling element, rubber bearing, rubber ring

6.1 Axial cutout

8 Hollow shaft, tube shaft, (hollow) drive shaft

8.1, 8.2 Hollow spaces within the hollow shaft

10 Tube axis

12 Constriction

14 (Press-in) sleeve

16 Rubber skin

18 Knocking nubs

What is claimed is:
 1. A hollow shaft assembly for a motor vehicle, thehollow shaft assembly comprising: a hollow shaft having an inner wallsurface defining an interior space and having a longitudinal axis; avibration absorber mounted in said interior space; said vibrationabsorber including an absorber mass and an elastic coupling element foroperatively connecting said absorber mass to said inner wall surface;said absorber mass being configured so as to be rotationally symmetricaland axially symmetrical with respect to said longitudinal axis; saidabsorber mass having a center region and being configured to have aconstriction at said center region for accommodating said elasticcoupling element therein; and, a slotted sleeve arranged between saidelastic coupling element and said inner wall surface of said hollowshaft.
 2. The hollow shaft assembly of claim 1, said slotted sleevebeing made of a poorly thermally conducting material.
 3. The hollowshaft assembly of claim 1, said elastic coupling element being made ofan elastomeric material.
 4. The hollow shaft assembly of claim 1, saidabsorber mass, said elastic coupling element and said slotted sleevebeing vulcanized to each other.
 5. The hollow shaft assembly of claim 1,said absorber mass, said elastic coupling element and said slottedsleeve being pressed to each other.
 6. The hollow shaft assembly ofclaim 1, said absorber mass, said elastic coupling element and saidslotted sleeve being joined to each other by adhesive.
 7. A hollow shaftassembly for a motor vehicle, the hollow shaft assembly comprising: ahollow shaft having an inner wall surface defining an interior space andhaving a longitudinal axis; a vibration absorber mounted in saidinterior space; said vibration absorber including an absorber mass andan elastic coupling element for operatively connecting said absorbermass to said inner wall surface; said absorber mass being configured soas to be rotationally symmetrical and axially symmetrical with respectto said longitudinal axis; said absorber mass having a center region andbeing configured to have a constriction at said center region foraccommodating said elastic coupling element therein; and, said vibrationabsorber being surrounded by a rubber skin and said absorber mass havingperipheral regions facing toward said inner wall surface at oppositeends of said center region and having a plurality of radial knockingnubs formed on each of said peripheral regions.
 8. The hollow shaftassembly of claim 7, said elastic coupling element having an axialcutout connecting the hollow spaces on respective ends of said vibrationabsorber to each other.
 9. The hollow shaft assembly of claim 8, saidaxial cutout being a bore.
 10. The hollow shaft assembly of claim 8,said axial cutout being a slot.
 11. A hollow shaft assembly for a motorvehicle, the hollow shaft assembly comprising: a hollow shaft having aninner wall surface defining an interior space and having a longitudinalaxis; a vibration absorber mounted in said interior space; saidvibration absorber including an absorber mass and an elastic couplingelement for operatively connecting said absorber mass to said inner wallsurface; said absorber mass being configured so as to be rotationallysymmetrical and axially symmetrical with respect to said longitudinalaxis; said absorber mass having a center region and being configured tohave a constriction at said center region for accommodating said elasticcoupling element therein; and, said vibration absorber having a resonantor inherent frequency which is matched in such a manner that saidresonant or inherent frequency of said vibration absorber is 55 to 85%of the resonant or inherent frequency of said hollow shaft without saidvibration absorber.